Smell from amp

[andy_wreck_fan]

Hm guys,I'm beginning to worry a little...
I'm new to ampbuilding and my express build smells strange....

It has normal crackle noises,still need to deal with that.

But when I turn it on and after 5-10mins I'm feeling strange smell...i turn it of then,look inside and nothing seems to be burning or anything....

could be the dust maybe burning on heat,cuz it's outside the cabinet? or OT(hope not cuz I cant afford new one atm)?

also,crackle in sound goes up only if u turn bass all the way up

[tubeswell]

Crackle is bad. Can mean a shot power tube, or worse, a shorted B+ frying the PT. You are probably not imagining that smell. (Carefully) check that your B+ rail isn't shorted to ground

[Structo]

That is anything but normal.

I realize English is not your primary language.

After the amplifier has been on for a while does the power transformer get hot to the touch?
Can you see any resistors that are getting hot/ discolored?

Is your PT big enough for the job?

[selloutrr]

is your center tap solid to ground? traces arching? turn off the lights and watch the amp in the dark.

[andy_wreck_fan]

Yep,I live in germany....

It's not getting any hotter than my Marshall's PT.
And PT is made for TW specs.

I checked and couldn't see anyting geting discolored.

Center tap?yep....

what does traces arching mean?


What I noticed is that under PT,where one of it's wires goes into chasis,1 string got little brown.....

[selloutrr]

string?

browning - possible your grounding is not tight to the chassis. vibration causes intermittent arching.

[xtian]

what does traces arching mean?

Sparking.

[andy_wreck_fan]

nope,not any sparking goin' on

I'm beginning to think that starting this build was a mistake

[Alexo]

nope,not any sparking goin' on

I'm beginning to think that starting this build was a mistake

Nooo!

Can you check for your current draw? Measure the voltage across each resistor in your power supply, calculate the current across each resistor using ohm's law and see if anything is off,

[tubeswell]

Hmmmm... If the voltages check out ok and there is no smoke coming from the PT, it could be something badly-soldered with voltage leakages. Is the 'crackle' like a low frequency spatter/rumble type of crackle through the speaker? If it is, try twiddling the EQ, presence and vol knobs and pulling the pre-amp tubes one by one to see if if stops/changes. (Come to think of it, I had this once in a 5F6A build: turned out to be a bad presence pot)

[andy_wreck_fan]

hm,presence acts as a bright switch from my exp(the higher setting the higher hiss,but that is same on my marshall,kinda)

but when i turn higher the bass control,crakling gets louder...



i checked grounding points,they are all tightly screwed...looked like 100 times through it and I cant notice a problem....

I think I will visit an amp tech to check it also....
It is my first build and I really like the way it sounds,but I lack a loads of knowledge to finish it for now

[Alexo]

I would...

poke around with a chopstick until you find a component that makes it crackle when you poke it.

Then re-flow the solder joint on that component.

...you always learn the most from your builds that go wrong!

[andy_wreck_fan]

I found a small brown area that looks burned on wire that goes to bias point....
here is an image...do you guys think this could be the smell place?

[IMG768]http://i56.tinypic.com/2lxa42b.jpg[/img]

[rp]

I found a small brown area that looks burned on wire that goes to bias point....

Looks like you did that with the soldering iron.

Is it an sharp acrid smell? Take a lighter and burn a little piece of wire, that is usually the smell of a short burning somewhere. You can even take a resistor with alligator clips and, attentively and carefully, plug it into a variac till it smokes. If that's the smell then you probably have a problem.

Put your nose right against your OT which is probably fine and inhale, is that the smell? A low, not sharp, dark mellow, smell, That's probably just the new transformers cooking and the lacquer gassing out. Are the trannies Chinese? Reports on the internet is that they smell more.

You might want to install a B+ fuse, it might just save you if you have a fault. Fast blow for a tube rectifier, but you'll have to use a less effective slow for ss.

[Richie]

more pics might help. Did you use the darker blue oxide resistors for screen grid resistors,or in the power section,or bleeders? Those can give off the burning electrical smell. The dark blue ones seem to be the only ones that do this. And they do it long before they have any burn marks.
Check voltages too, that can sometimes clue in where the problem is.